Cannabis sativa preparations have long been known as therapeutic agents to treat various diseases (Mechoulam, R., “Cannabinoids as Therapeutic Agents” CRC Press, Boca Raton, Fla. 1-19, 1986). The native active constituent, delta 9-tetrahydrocannabinol (Δ9-THC), is prescribed today, under the generic name dronabinol, as an anti-emetic and for enhancement of appetite, mainly in AIDS patients. However, separation between the clinically undesirable psychotropic effects and the therapeutically desirable effects on the peripheral nervous systems, the cardiovascular system, the immune and endocrine system is problematic. The discovery of two cannabinoid receptors, CB1 and CB2, has helped to elucidate the diverse cannabinoid effects.
The CB1 receptor has been cloned from rat, mouse, and human tissues and exhibits 97-99% amino acid sequence identity across species. The CB2 receptor exhibits 48% homology with the CB1 receptor (A. C. Howlett et al. Pharmacological Reviews 2002, 54, 161-202). The structures of both receptors are consistent with seven transmembrane G-protein coupled receptors. In addition, both receptors exert their effect by negative regulation of adenylyl cyclase activity through pertussis toxin-sensitive GTP-binding proteins. They have been shown to activate the mitogen activated protein kinase (MAPK) in certain cell types (Parolaro, D., Life Sci. 1999, 65, 637-44).
The CB1 receptor is expressed mainly in the central nervous systems (CNS) and to a lesser extent in other tissues including, for example, gastrointestinal tissues, immune cells, reproductive organs, heart, lung, urinary bladder and adrenal gland. The CB2 receptor is expressed mostly in peripheral tissue associated with immune functions including, for example, macrophages, B cells, T cells and mast cells, as well as in peripheral nerve terminals (Pertwee, R. G., Prog. Neurobiol. 2001, 63, 569-611). The central distribution pattern of CB1 receptors accounts for several unwanted pharmacological properties of cannabinoids, such as impaired cognition and memory, altered control of motor function, and psychotropic and other neurobehavioral effects. CB1 receptors are also found on pain pathways in brain, spinal cord and at the peripheral terminals of primary sensory neurons (A. S. Rice, Curr. Opin. Investig. Drugs 2001 2(3), 399-414).
CB1 knockout mice have been shown to be unresponsive to cannabinoids in behavioral assays providing molecular evidence that the psychotropic effects, including sedation, hallucinations and antinociception are manifested through the activation of the CB1 receptor, present primarily in the CNS. Analysis of the CB2 knockout mouse has corroborated the evidence for the function of CB2 receptors in modulating the immune system. The CB2 receptor does not affect immune cell development and differentiation as determined by FACS analysis of cells from the spleen, lymph node and thymus from CB2 knockout mice. Further studies in these mice have shown that the immunosuppressive effects of Δ9-THC are mediated by the CB2 receptor.
Some cannabinoid receptor agonists have been shown to produce potent antinociception with equivalent efficacy to morphine in animal models of acute pain, persistent inflammatory pain, and neuropathic pain. They have also been reported to induce a number of unwanted CNS side effects. Furthermore, the known cannabinoid receptor agonists are in general highly lipophilic and insoluble in water. There is thus a need for cannabinoid receptor agonists with improved properties for uses as therapeutic agents.
Known CB1 cannabinoid receptor agonists produce a characteristic profile of in vivo effects in mice, including suppression of spontaneous activity, antinociception, hypothermia, and catalepsy. Measurement of these four properties, commonly referred to as the tetrad test, has played a key role in establishing the structure-activity relationship of cannabinoids and cannabimimetics acting at CB1 receptors. Catalepsy in mice is indicative of CB1 activation and predictive of cannabinoid psychoactivity. Pertwee showed a correlation between catalepsy in the ring test in mice and the previously validated dog static ataxia model (R. G. Pertwee, Br. J. Pharmacology 1972, 46, 753-763). Therefore, catalepsy in mice is viewed as excellent predictor of CNS effects in humans (D. R. Compton, Marijuana: An International Research Report 7, 213-218, 1987; E. W. Gill and G. Jones, Biochem. Pharmacol. 21, 2237-2248, 1972; E. W. Gill et al. Nature 228, 134-136, 1970).
Efforts have been made to separate therapeutic effects from undesirable CNS side effects by increasing the selectivity for the CB2 receptor, thereby leading to efforts to design compounds with selectivity for the CB2 receptor over the CB1 receptor. These compounds would be predicted to lack side effects even if they penetrate the CNS because they would not activate the CB1 receptors in the CNS (Malan, T. Philip, Jr. et al. “CB2 cannabinoid receptor agonists: pain relief without psychoactive effects?” Curr Op. Pharm. 2003, 3(1), 62-67; WO2004/017920).
Recent studies have identified CB2 selective inverse agonists with antiedema effects in vivo (Iwamura et al., J. Pharm. Exp. Ther. 2001, 420-425; Lavey et al. Bioorg. Med. Chem. Lett. 2005, 783-786), suggesting an involvement of CB2 selective inverse agonists in inflammatory processes and the pharmacological efficacy of CB2 inverse agonists by themselves.
Lunn, et al. (ICRS 15th Annual Symposium of the Cannabinoids, Clearwater Beach, Fla., Jun. 24-27, 2005) have reported that CB2 receptor-selective inverse agonists are capable of altering cellular chemotaxis mediated by either cannabinoids or chemokines, both in vivo and in vitro. They have reported that administration of these compounds can decrease allergic eosinophilia in animal models for asthma.
Other research has shown that pharmacological antagonists of CB1 and CB2 receptors prevented ovariectomy-induced bone loss in vivo and caused osteoclast inhibition in vitro by promoting osteoclast apoptosis and inhibiting production of several osteoclast survival factors. These studies show that the CB1 receptor has a role in the regulation of bone mass and ovariectomy-induced bone loss and that CB1- and CB2-selective cannabinoid receptor antagonists are a new class of osteoclast inhibitors that may be of value in the treatment of osteoporosis and other bone diseases (A. I Idris, et al., Nature Medicine, 2005, 11(7), 774-79).
There is considerable interest in developing new cannabimimetic compounds possessing preferentially high affinity for the CB2 receptor. Such compounds that preferentially stimulate the CB2 receptor, directly or indirectly, may provide clinically useful effects without unwanted effects on the subject's central nervous system and can offer a rational therapeutic approach to a variety of disease states. The present invention is directed to these and other important ends.